Diabetes and Diabetes Treatment Not Linked to Thyroid Cancer in Postmenopausal Women

Commentary by lead author Juhua Luo, PhD and Megan R. Haymart, MD

Diabetes and diabetes treatment were not linked to the risk of thyroid cancer in a large prospective study involving nearly 150,000 postmenopausal women. The findings were published in the March issue of TheJournal of Clinical Endocrinology and Metabolism.

“There is still much to learn about what causes thyroid cancer,” said lead author Juhua Luo, PhD, Associate Professor in the Department of Epidemiology and Biostatistics in the School of Public Health at Indiana University in Bloomington, IN. “Although diabetes was not linked to thyroid cancer in our study, diabetes is a major risk factor for cardiovascular disease and some other cancers, and prevention of diabetes is still very important.”

“Although there had been speculation that the thyroid cancer epidemic was not independent from the diabetes epidemic, this data suggest that they are two unrelated phenomena,” commented Megan R. Haymart, MD, who is Assistant Professor of Medicine in the Divisions of Metabolism, Endocrinology, & Diabetes and Hematology/Oncology at the University of Michigan Health System in Ann Arbor, MI. “Physicians should not screen diabetic patients for thyroid cancer as their risk is likely no different than the population at large, and in general thyroid cancer screening is not recommended,” Dr. Haymart added.

Study Rationale
“The impetus for this study was based on the following background and rationales: (1) the incidence rate of thyroid cancer has been increasing; (2) currently, little is known about the etiology of thyroid cancer; (3) higher body mass index (BMI) was found to be associated with an increased risk of thyroid cancer; (4) BMI is a major risk factor for diabetes,” Dr. Luo said. “Thus, we proposed that it is possible that patients with type 2 diabetes may have an increased risk of thyroid cancer.”

Data Derived From the Women’s Health Initiative
The authors examined data from 147,934 women enrolled in the Women’s Health Initiative. Over a median follow-up of 15.9 years, 391 women developed incident thyroid cancers.

In addition, the risk of thyroid cancer was not significantly associated with the type of diabetes treatment used, with nonsignificant hazard ratios ranging from 1.13-1.57 depending on the agent used. Furthermore, thyroid cancer risk was not linked to longer duration of diabetes (ie, ≥6 years; hazard ratio, 1.18).

No Relationship Found Between Diabetes and Thyroid Cancer Incidence
“Although not definitive, this is a strong study suggesting no relationship between diabetes mellitus and thyroid cancer incidence,” Dr. Haymart said. “Strengths [of the study] include the large sample size, ample follow-up, comprehensive set of covariates, and use of sensitivity analysis,” Dr. Haymart added.

“It is hard to say that findings from any one epidemiological study can provide definitive evidence for this conclusion,” Dr. Luo noted. “Our study was conducted among postmenopausal women. More studies are needed to confirm our findings.”